Annual report pursuant to Section 13 and 15(d)

INVENTORIES (Narrative) (Details)

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INVENTORIES (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Inventory [Line Items]    
Cost of Goods Sold $ 6.2 $ 8.8
LCM inventory adjustment 1.8 0.0
U.S. Iron Ore [Member]    
Inventory [Line Items]    
Inventory, LIFO Reserve $ 96.2 $ 78.5